In the formation of bottles and similar containers from thermoplastic materials in blow molding operations, various techniques have been used to form an integral container base having a support surface to enable the container to stand upright in a relatively stable condition. These techniques include, for example, the use of movable mold components, such as pivotal arms with convex mold surfaces, or telescopic sleeves which may be inserted within the blow mold cavity after the blowing operation to convert the convex bottle bottom into a concave shape with a support surface. Most of these techniques inherently include various disadvantages, such as the requirement of additional mold parts and requiring additional operational steps which slow the overall blow molding cycle. Problems have also arisen in prior attempts to form a pressure bottom for a plastic bottle to hold liquids under pressure, such as carbonated beverages, a typical such bottom being similar to the bottom of a glass champagne bottle. This particular design has been undesirable because the concave bottom portion tends to be forced outwardly to a convex configuration under elevated internal pressures. This problem may be solved by increasing the wall thickness of bottle bottom, but this is undesirable from a material usage and cost standpoint. Additionally, the champagne bottom is undesirable because the annular bottom support surface necessarily has a dimension that is smaller than the maximum radial dimension of the bottle wall, and therefore does not provide as much stability as may be desired for maintaining the bottle in a stable upright position.
To overcome these particular problems, separate support bases have been mounted on the bottom of bottles, but these separate members have previously included their own shortcomings. For example, some support bases have been designed for easy assembly, but become removed just as easily during handling. Other bases have been designed for interference fits to alleviate the removal problem, but difficulties have been encountered because a pocket of air between the bottle bottom and the base provides a resistance to their assembly. A first attempt to remedy this particular problem included the provision of an air escape opening in the bottom of the base; however, that opening provided a passageway for liquids to enter the space between the bottle bottom and base, resulting in undesirable bacteria growth.
Accordingly, the prior art does not provide a separate container base which can be easily mounted on the container bottom and provide a water-tight seal.